1. Field of the Invention
This invention relates to a record material adapted for use in reading by an optical character- or mark-reading machine.
There are known various kinds of recording systems utilizing the colorforming reaction between a colorless or substantially colorless chromogenic material and an electron accepting acidic reactant material by the medium of mechanical, heat, electric or light energy. Among them there are included a pressure sensitive record sheet, a heat sensitive record sheet, an electrothermal record sheet, an ultrasonic record sheet, an electron beam record sheet, an electrostatic record sheet and a photosensitive record sheet. The colorless chromogenic materials of these kinds also find their usefulness in photosensitive printing material, typewriter ribbons, ball-point pen ink, crayon and stamp ink.
On the other hand, various optical character- or mark-reading machines are used for reading the record images developed on a record material. Record images developed on the conventional record materials such as those of black, blue, red and green can be read by optical reading machines which are capable of reading for the visible wavelength range of 400 nm to 700 nm, but those record images cannot be detected by optical reading machines which are capable of reading for the infrared wavelength range of 700 nm to 900 nm because those images function not as read colors but as dropout colors.
Many of record materials which are processed for reading by optical reading machines are used as various business forms on which ruled lines, column frames, item indications, and other letters for explanation, etc. are usually pre-printed. Those pre-printed markings must be printed by ink of a dropout color so that erroneous reading by an optical reading machine may not be caused. In case where an optical reading machine having a visible wavelength reading range is used, an extremely careful consideration for selecting the kind and amount of the ink used is required to ensure a good readability. In order to avoid careful consideration for selecting the ink used, there has been proposed the utilization of various optical reading machines having infrared wavelength reading ranges.
Recently it has been proposed to utilize phthalide compounds having two vinyl linkages as substantially colorless chromogenic material which are adapted for optical reading with near infrared rays.
However, if any of those compounds is solely used as a colorless chromogenic material for a record material, though the color images developed upon contact with an electron accepting reacting material are remarkably absorptive of near infrared rays, the chromogenic material is relatively or appreciably absorptive of near infrared rays even before color developing. Accordingly, when such compounds like those are used e.g. for heat sensitive record material erroneous reading often occurs with use of an optical reading machine having a near infrared wavelength reading range since there is only poor contrast between color images developed and the background thereof. On the other hand, the color images obtained with use of such phthalide compounds having two vinyl linkages are substantially illegible with use of an optical reading machine having a visible wavelength reading range since those color images shows poor absorption of visible rays in addition to the fact that those color images are only visible in a faint blue green color and accordingly reduce the commercial value of the record material.
It is the principal object of the invention to provide a record material which can develop record images in such a visible color as black, blue, red or green and is also adapted to optical reading machines having wide reading ranges over visible and infrared wavelengths.
2. Description of the Prior Art
U.S. Pat. No. 4,020,056 issued Apr. 26, 1977 and U.S. Pat. No. 4,107,428 issued Aug. 15, 1978 discloses certain kinds of phthalide derivative chromogenic compounds having two vinyl linkages which compounds may be converted to colored forms upon reactive contact with acidic material. The color images developed have near infrared color response. EP Application No. 82301885.8 (EP Publication No. 62544) discloses another phthalide compounds in which the color images when developed therefrom have a good light resistance and show a good absorption for infrared rays.